[alsa-devel] [PATCH - alsa-lib 1/1] Patch for two bugs in snd_pcm_area_silence().
From: furrywolf alsa2@bushytails.net
First, after silencing the buffer 64 bits at a time, any remaining samples need to be silenced by the following width-specific code. However, instead of silencing the end of the buffer, the code instead re-silences the start of the buffer, leaving the end unsilenced. To fix this, update the pointer used by the width-specific code to point to the end of the area just silenced, instead of leaving it pointing to the start of the buffer.
Second, the code for 24 bit samples can only silence a single sample, as there's no loop for multiple samples as with other formats. To fix this, add a loop similar to the ones used for every other width.
The symptoms of these bugs are random data at the end of every supposedly silenced buffer with certain format/buffer size combinations, resulting in pops and noise.
Signed-off-by: furrywolf alsa2@bushytails.net
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index 69d7d66..1753cda 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -2955,6 +2955,7 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes *dstp++ = silence; if (samples == 0) return 0; + dst = (char *)dstp; } dst_step = dst_area->step / 8; switch (width) { @@ -2996,16 +2997,20 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes } break; } - case 24: + case 24: { + while (samples-- > 0) { #ifdef SNDRV_LITTLE_ENDIAN - *(dst + 0) = silence >> 0; - *(dst + 1) = silence >> 8; - *(dst + 2) = silence >> 16; + *(dst + 0) = silence >> 0; + *(dst + 1) = silence >> 8; + *(dst + 2) = silence >> 16; #else - *(dst + 2) = silence >> 0; - *(dst + 1) = silence >> 8; - *(dst + 0) = silence >> 16; + *(dst + 2) = silence >> 0; + *(dst + 1) = silence >> 8; + *(dst + 0) = silence >> 16; #endif + dst += dst_step; + } + } break; case 32: { uint32_t sil = silence;
Hi,
On Jan 21 2018 12:27, alsa2@bushytails.net wrote:
From: furrywolf alsa2@bushytails.net
First, after silencing the buffer 64 bits at a time, any remaining samples need to be silenced by the following width-specific code. However, instead of silencing the end of the buffer, the code instead re-silences the start of the buffer, leaving the end unsilenced. To fix this, update the pointer used by the width-specific code to point to the end of the area just silenced, instead of leaving it pointing to the start of the buffer.
Second, the code for 24 bit samples can only silence a single sample, as there's no loop for multiple samples as with other formats. To fix this, add a loop similar to the ones used for every other width.
The symptoms of these bugs are random data at the end of every supposedly silenced buffer with certain format/buffer size combinations, resulting in pops and noise.
Signed-off-by: furrywolf alsa2@bushytails.net
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index 69d7d66..1753cda 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -2955,6 +2955,7 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes *dstp++ = silence; if (samples == 0) return 0;
dst = (char *)dstp;@@ -2996,16 +2997,20 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes } break; }
- case 24:
- case 24: {
while (samples-- > 0) {
*(dst + 0) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 2) = silence >> 16;
*(dst + 0) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 2) = silence >> 16;
*(dst + 2) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 0) = silence >> 16;
*(dst + 2) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 0) = silence >> 16;dst += dst_step;}- } break; case 32: { uint32_t sil = silence;
I'm under reviewing this patch, but need a bit more time (I'm writing test program to check these functions.).
However, as you noted, this patch includes two issues. There's a space to consider about splitting this into two patches, each of which handles each issue you addressed.
Regards
Takashi Sakamoto
Hi furrywolf and Iwa-san,
To review this patch, I wrote a program to test two functions (snd_pcm_areas_silence() and snd_pcm_area_silence()) in alsa-lib. https://github.com/takaswie/practices/blob/topic/alsa-lib-test/alsa-lib/test...
After reviewing, I concluded that this patch is preferable to fix the addressed bugs. However, this patch is not enough yet and we have rest of the bugs.
To maintainers, would you please apply this patch to master of alsa-lib repository?
On Jan 21 2018 12:27, alsa2@bushytails.net wrote:
From: furrywolf alsa2@bushytails.net
First, after silencing the buffer 64 bits at a time, any remaining samples need to be silenced by the following width-specific code. However, instead of silencing the end of the buffer, the code instead re-silences the start of the buffer, leaving the end unsilenced. To fix this, update the pointer used by the width-specific code to point to the end of the area just silenced, instead of leaving it pointing to the start of the buffer.
Second, the code for 24 bit samples can only silence a single sample, as there's no loop for multiple samples as with other formats. To fix this, add a loop similar to the ones used for every other width.
The symptoms of these bugs are random data at the end of every supposedly silenced buffer with certain format/buffer size combinations, resulting in pops and noise.
Signed-off-by: furrywolf alsa2@bushytails.net
diff --git a/src/pcm/pcm.c b/src/pcm/pcm.c index 69d7d66..1753cda 100644 --- a/src/pcm/pcm.c +++ b/src/pcm/pcm.c @@ -2955,6 +2955,7 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes *dstp++ = silence; if (samples == 0) return 0;
dst = (char *)dstp;
This fixes a bug of 'snd_pcm_area_silence()' in several cases. In this bug, the caller gets PCM buffers with silent samples up to the number of frames according to parameters on given 'dst_areas', 'dst_offset', 'channels' and 'format'. In most cases, quite less number of silent samples are written than given 'frames'.
After applying this change, in this point, the program passed all tests.
@@ -2996,16 +2997,20 @@ int snd_pcm_area_silence(const snd_pcm_channel_area_t *dst_area, snd_pcm_uframes } break; }
- case 24:
- case 24: {
while (samples-- > 0) {
*(dst + 0) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 2) = silence >> 16;
*(dst + 0) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 2) = silence >> 16;
*(dst + 2) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 0) = silence >> 16;
*(dst + 2) = silence >> 0;*(dst + 1) = silence >> 8;*(dst + 0) = silence >> 16;dst += dst_step;}- } break; case 32: { uint32_t sil = silence;
Before applying this patch, the test program fails for below 24 bit sample formats: * S24_3LE * S24_3BE * U24_3LE * U24_3BE * S20_3LE * S20_3BE * U20_3LE * U20_3BE * S18_3LE * S18_3BE * U18_3LE * U18_3BE
After applying this change, calls of the library API for any 'signed' format of the above formats are successes at the test, however, any 'unsigned' formats aren't. Your change is preferrable but not enough to fix this bug, unfortunately...
Anyway, I appreciate your attempt to fix this library API. I'll do further investigation to break down relevant bugs of this library API, then I'm going to fix it, perhaps work for refactoring with my test program.
Regards
Takashi Sakamoto
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Takashi Sakamoto